This invention relates to an air spring which is disposed between a vehicle wheel and the body of a two-wheeled vehicle in order to absorb vibration.
The provision of an air spring between a vehicle wheel and vehicle body in modern bicycles improves riding comfort by absorbing road surface vibrations when the bicycle is running.
Various types of air springs have been proposed and an example thereof is shown in FIG. 9.
This type of air spring comprises an air chamber A which is partitioned by a piston 103 in a cylinder 101 and an air chamber B in a tank 110 which is separated from cylinder 101. The air chambers A and B which are filled with pressurized air connected by a passage 108. The air chambers A, B are connected and disconnected as a result of switching operations performed by a switch valve 109 which is provided in the passage 108 connecting the chambers.
When the air chambers A, B are connected, the effective volume of the air spring is increased with the result that a low spring force is applied. When the air chambers A, B are disconnected, a small effective volume corresponding to only the air chamber a results in a high spring force.
For example, a piston rod 102 is connected to the vehicle wheel and the cylinder 101 is connected to the vehicle body in this air spring. An air chamber C disposed opposite the piston 103 is at atmospheric pressure.
A bicycle comprising an air spring allows the rider to switch the switch valve 109 in order to select a hard ride based on a high spring force or a soft ride based on a low spring force when riding the bicycle.
However a tank 110 which is separate from the cylinder 101 is required in the air spring in order to switch between a high and low spring force. Moreover the capacity of this tank 110 must be large in order to increase the differential variation (width thereof) of the spring force resulting from switching.
As a result, the problem has arisen that the overall size of the spring is increased.
The object of the present invention is to provide an air spring enabling two clearly distinct spring characteristics in a compact unit.
In order to achieve above the object, the invention provides an air spring for a two-wheeled vehicle, the air spring being disposed between a vehicle body and a vehicle wheel. The air spring comprises a piston which slides in a cylinder member, a rod member which is engaged with the piston, a rod-side air chamber and a piston-side air chamber which are partitioned in the cylinder member by the piston and are filled with compressed air, a passage which connects the two air chambers, and a switch valve which opens and closes the passage.